Hydrotalcite is an inorganic compound containing magnesium, zinc and aluminum, and it is known from WO 99/01509, Japanese kokoku Publication Sho-46-2280, Japanese kokoku Publication Sho-47-32198, Japanese kokoku Publication. Sho-48-29477, Japanese kokoku Publication Sho-50-30039, Japanese kokoku Publication Sho-51-29129 and Japanese Kokai Publication Sho-55-80445, that by using it as an additive of synthetic resins for general purpose such as polyolefin, polyvinyl chloride and the like, properties as a heat stabilizer of resin or an acid-acceptor of resin can be attained. It is known that a resin composition containing the hydrotalcite is particularly superior in a thermal insulating property and thermal stability and this resin composition can be used in applications such as a film for agricultural uses and a resin for covering wires.
But, when the hydrotalcite is mixed into a polyolefin resin or a copolymer thereof, a problem that die drool or coloring (yellowing) occurs by being subjected to a step of heating for processing arises. Therefore, it has been desired to decrease the occurrence of die drool and coloring resulting from the hydrotalcite.
Further, as a film for agricultural uses, polyolefinic resin films such as a polyvinyl chloride film, a polyolefin film and an ethylene-vinyl acetate copolymer film are mainly used for houses or tunnels in protected horticulture. The performance required of such a film for agricultural uses varies with its use, applications and subjects of crops, and therefore various properties other than heat resistance may be required. However, in some cases, specific properties are deteriorated or other properties are not improved, depending on the additional amount of hydrotalcite.
For example, the films for agricultural uses are required to have properties such as weathering resistance (performance capable of resisting a long-term use in the sunny outdoors), an anti-fogging property (performance of preventing a phenomenon in which an inner surface of a covering film is covered with fine sweat through condensation due to high humidity in houses or tunnels and its transparency is deteriorated), a thermal insulating property (performance of maintaining temperature in facilities high during the night) and a translucency (transparency). With respect to a synthetic resin composition, containing the hydrotalcite, for polyolefin films for agricultural uses, it is known that when an amount of the hydrotalcite is increased, a white discoloration by water due to rainwater, moisture and sweat in uses further occurs as the hydrotalcite content in a film increases. Thus, it has been desired to inhibit a white discoloration by water of a polyolefin film for agricultural uses.
And, when the hydrotalcite is added to a vinyl chloride resin film in a relatively large amount, a blooming (effusion of powder) to the surface of a film arises and therefore countermeasures for this have been requested.
Further, the hydrotalcite is also used as a stabilizer of a vinyl chloride resin for covering wires in place of a lead stabilizer, use of which is not preferred from the view point of an environmental impact. But, when the conventional hydrotalcite having a sodium content of more than 100 ppm is used, there is a problem that the electric resistance (volume resistivity=VR) of the vinyl chloride resin is reduced compared with the case of using the lead stabilizer. Thus, there has been required such hydrotalcite that a vinyl chloride resin composition having the electric resistance which is equal to that in using the lead stabilizer can be obtained.